According to well known prior art IC (integrated circuit) packaging methodologies, semiconductor dice are singulated and mounted using epoxy or other conventional means onto respective die attach pads of a leadframe strip. Traditional QFP (Quad Flat Pack) packages incorporate inner leads which function as lands for wire bonding the semiconductor die bond pads. These inner leads typically require mold locking features to ensure proper positioning of the leadframe strip during subsequent molding to encapsulate the package. The inner leads terminate in outer leads that are bent down to contact a mother board, thereby limiting the package density of such prior art devices.
In order to overcome these and other disadvantages of the prior art, the Applicants previously developed a Leadless Plastic Chip Carrier (LPCC). According to Applicants' LPCC fabrication methodology, a leadframe strip is provided for supporting up to several hundred devices. Singulated IC dice are placed on the strip die attach pads using conventional die mount and epoxy techniques. After curing of the epoxy, the dice are gold wire bonded to peripheral internal leads. The leadframe strip is then molded in plastic or resin using a modified mold in which the bottom cavity is a flat plate. In the resulting molded package, the die pad and leadframe inner leads are exposed. By exposing the bottom of the die attach pad, mold delamination at the bottom of the die attach pad is inhibited, thereby increasing the moisture sensitivity performance. Also, thermal performance of the IC package is improved by providing a direct thermal path from the exposed die attach pad to the motherboard. By exposing the leadframe inner leads, the requirement for mold locking features is eliminated and no external lead standoff is necessary, thereby increasing device density and reducing package thickness over prior art methodologies. The exposed inner leadframe leads function as solder pads for motherboard assembly such that less gold wire bonding is required as compared to prior art methodologies, thereby improving electrical performance in terms of board level parasitics and enhancing design flexibility over prior art packages (i.e. custom trim tools and form tools are not required). These and several other advantages of Applicants' own prior art LPCC process are detailed in Applicants' U.S. Pat. No. 6,229,200, issued May 8, 2001, the entire contents of which are incorporated herein by reference.
Applicant's LPCC production methodology utilizes saw singulation to isolate the perimeter I/O row as well as multi-row partial lead isolation. Specifically, the leadframe strip is mounted to a wafer saw ring using adhesive tape and saw-singulated using a conventional wafer saw. The singulation is guided by a pattern formed by fiducial marks on the second side (bottom) of the leadframe strip. Also, special mold processing techniques are used to keep the mold from bleeding onto the functional pad area and inhibiting electrical contact. Specifically, the exposed die pad surface is required to be deflashed after molding to remove any molding compound residue and thereby allow the exposed leads and die attach pad to serve as solder pads for attachment to the motherboard.
According to Applicant's own U.S. Pat. No. 6,498,099, issued Dec. 24, 2002, the contents of which are incorporated herein by reference, a localized etch process is provided for the improved manufacture of the LPCC IC package. The leadframe strip is subjected to a partial etch on one or both of the top and bottom sides in order to create a pattern of contact pads and a die attach pad.
Further improvements in IC packages are driven by industry demands for increased electrical performance and decreased size and cost of manufacture. With continued improvements in electrical performance and decreasing package size, improvements in thermal performance are needed. In particular, further improvements in heat dissipation are desirable, particularly in high power applications.